The present invention relates to recording, and more particularly to methods and circuits for reducing beats.
In order to achieve a high dynamic range and good signal to noise ratio, it is known to separately record luminance and chrominance components of a composite video signal on adjacent tracks. The chroma signal is baseband recorded, which requires a bias signal for linearization, while the luminance signal is FM recorded, which does not require a bias. If a fixed frequency bias is used for the chroma recording, the bias signal will beat with the FM luminance signal during both recording (due to inductive coupling between recording heads) and playback (due to the chroma head picking up the recorded bias frequency and inductively coupling it to the luminance head). This will alter the phase of the FM luminance signal, causing variations in it across the display tube after demodulation. One possibility is to increase the bias frequency so that the chroma head will not pick up the bias signal during playback. This still leaves the beat generation problem during recording.
One way that has been tried to overcome this problem is to use the FM luminance carrier as the chroma signal recording bias. This eliminates the beating problem during recording since the bias and carrier have the same frequency. However, during playback the chroma head will pick up the bias signal and inductively couple it to the luminance head. Due to slight timing difference between the chroma and luminance tracks, the induced bias signal and the FM carrier reproduced from the luminance track will have phase differences causing phase shift in the FM carrier and thus distortion in the reproduced picture. To overcome his problem, it is known to make the chroma head gap longer so it will not pick up during playback the FM signal used as a bias signal. However, since the chroma and luminance heads are now different, manufacturing costs are higher, and they have a different phase response, which must be electrically compensated.
It is therefore desirable to have a recording system that eliminates beats during both record and playback operations without increasing complexity.